JPH06200743A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] When desorbing HC from adsorbents, NOx
Allows processing without increasing emissions. [Structure] When the engine is cold, the exhaust gas is guided to an adsorbent 7 to adsorb HC in the exhaust gas. At a time after the completion of warming up, the exhaust gas is guided to the adsorbent 7 again to desorb HC, and the desorbed HC is purified by the main catalyst 4 on the downstream side. During this desorption process, secondary air is introduced upstream of the main catalyst 4 by the air pump 9 and the fuel injection amount from the fuel injection valve 15 to the engine 1 is increased to enrich the air-fuel ratio of the engine intake air-fuel mixture. , The air-fuel ratio at the inlet of the main catalyst 4 is brought close to the stoichiometric air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to adsorbing hydrocarbons (hereinafter referred to as "HC") in exhaust gas to an adsorbent when the engine is cold and desorbing the hydrocarbon after completion of warming up. The present invention relates to an exhaust gas purification device that is processed by a method.

[0002]

2. Description of the Related Art Immediately after starting an internal combustion engine, the exhaust gas from the engine contains a relatively large amount of HC, and the temperature of a catalyst for purifying exhaust gas does not reach an activation temperature, so that it is difficult to purify HC. Therefore, for example, JP-A-55-10171
As disclosed in Japanese Patent Publication No. 5 and the like, a sub passage is provided in parallel with the main passage of the exhaust passage upstream of the catalyst for purifying exhaust gas, and the adsorbent for HC is interposed in the sub passage. A valve device for controlling the flow of exhaust gas to the passage and the sub-passage is provided, and by controlling this valve device, all of the exhaust gas is circulated to the adsorbent when the engine is cold, and HC in the exhaust gas is used as the adsorbent. Adsorbed. Then, at a time after the completion of warming up, HC is desorbed from the adsorbent, and the desorbed HC is purified by the downstream catalyst.

In addition, at the time of desorption treatment of HC, in order to improve the catalyst purification performance, that is, to prevent the deterioration of the HC conversion rate due to the enrichment of the atmosphere in the catalyst and the temperature decrease, a secondary air inlet provided upstream of the catalyst is used. It is also known that it is effective to introduce a large amount of secondary air to activate combustion in the catalyst.

[0004]

However, in such a conventional exhaust gas purification apparatus, by introducing secondary air upstream of the catalyst during the HC desorption process, combustion is activated and HC conversion occurs. Although the rate is improved, there is a problem that the atmosphere in the catalyst becomes lean, NOx is not sufficiently purified, and the NOx emission amount increases.

The present invention has been made by paying attention to such a conventional problem, and a good HC desorption process can be performed during the desorption process and when the secondary air is introduced without increasing the NOx emission amount. The purpose is to enable.

[0006]

Therefore, according to the present invention, as shown in FIG. 1, an auxiliary passage is provided in parallel with the main passage of the exhaust passage upstream of the catalyst for purifying the exhaust gas. A valve device that controls the flow of exhaust gas to the main passage and the sub-passage while interposing a hydrocarbon adsorbent in the passage, and by controlling this valve device, all of the exhaust gas is adsorbed when the engine is cold. In an exhaust gas purifying apparatus for an internal combustion engine, comprising: a control device for adsorbing hydrocarbons in exhaust gas by flowing into the adsorbent and desorbing hydrocarbons by flowing at least a part of exhaust gas to an adsorbent at a time after completion of warm-up. When desorbing hydrocarbons from the adsorbent by the control device, desorption secondary air introducing means for introducing secondary air to the catalyst is provided, and at the time of desorption,
The desorption air-fuel ratio enrichment means for controlling the air-fuel ratio of the engine intake air-fuel mixture to the rich side is provided.

Alternatively, in the present invention, instead of the air-fuel ratio enrichment means for desorption, at the time of desorption, a desorption control for controlling the amount of exhaust gas recirculation (hereinafter referred to as "EGR") recirculated from the exhaust passage to the intake passage to the increasing side. A configuration is provided in which the EGR amount increasing means at the time of separation is provided (see the dotted line portion in FIG. 1).

[0008]

In the above structure, after warming up, at least a part of the exhaust gas is circulated to the adsorbent to desorb the HC from the adsorbent, and the desorbed HC is purified by the downstream catalyst. While introducing the secondary air into the catalyst, the air-fuel ratio of the engine intake air-fuel mixture is controlled to the rich side.

That is, during the desorption treatment,
Secondary air is introduced by controlling the air-fuel ratio of the engine intake air-fuel mixture to the rich side while introducing a sufficient amount of secondary air to obtain active combustion in the catalyst to improve the HC purification performance of the catalyst. By introducing the above, the atmosphere becomes lean and the NOx purification performance is lowered, and the catalyst inlet air-fuel ratio is brought close to the stoichiometric air-fuel ratio, and the purification performance of the three components (HC, CO, NOx) in the catalyst is kept good. That is, while supplying the secondary air to increase the absolute amount of oxygen, the catalyst inlet air-fuel ratio can be brought close to the stoichiometric air-fuel ratio, and active combustion in the catalyst can be maintained to prevent the temperature drop of the catalyst. , NOx emissions can be reduced. At the same time, the atmosphere in the combustion chamber becomes rich,
The amount of NOx generated from the engine is also reduced.

Further, instead of controlling the air-fuel ratio of the engine intake air-fuel mixture to the rich side, the EGR rate may be increased to reduce the NOx generated from the engine.

[0011]

EXAMPLES Examples of the present invention will be described below. FIG. 2 shows the system configuration of one embodiment. The exhaust passage 2 of the engine 1 is provided with a pre-catalyst 3 and a main catalyst 4 for exhaust gas purification.

Between the pre-catalyst 3 and the main catalyst 4, the exhaust passage 2 is branched into a main passage 5 and a sub passage 6, and the sub passage 6 has an adsorbent 7 for HC containing activated carbon or zeolite as a main component. Is installed. And the main passage 5
As a valve device for controlling the flow of exhaust gas to the sub-passage 6 and the sub-passage 6, an electromagnetic flow passage switching valve 8 is provided at the downstream merging portion of the main passage 5 and the sub-passage 6. The flow path switching valve may be provided at the upstream branch portion of the main passage 5 and the sub passage 6.

A secondary air inlet 10 from an air pump 9 is provided upstream (inlet) of the main catalyst 4.
Here, the flow path switching valve 8 and the air pump 9 are
Control unit 11 as adsorption / desorption control device
Controlled by. The control unit 11 has a built-in microcomputer and includes an adsorbent 7
Signals are input from an adsorbent inlet exhaust temperature sensor 12 that detects the exhaust temperature Ta on the inlet side of the main catalyst, a main catalyst outlet exhaust temperature sensor 13 that detects the exhaust temperature Te on the outlet side of the main catalyst 4, etc., and will be described later. Arithmetic processing is performed according to the flowchart.

On the other hand, an electromagnetic fuel injection valve 15 is provided for each cylinder in the manifold portion of the intake passage 14 of the engine 1, and each fuel injection valve 15 is controlled by a control unit 16 for controlling the engine. Control unit 16
Includes a microcomputer, to which information such as the engine intake air flow rate Q and the engine speed N is input, and the engine intake air-fuel mixture is supplied via the O ₂ concentration in the exhaust gas from the engine 1. O ₂ which can detect rich / lean air-fuel ratio
The signal from the sensor 17 is input, and arithmetic processing is performed as follows. That is, the basic fuel injection amount Tp = K × Q / N (K is a constant) is calculated from the engine intake air flow rate Q and the engine speed N, and proportional integral control (K is a constant) based on a signal from the O ₂ sensor 17 ( The fuel injection amount T is corrected by the air-fuel ratio feedback correction coefficient α set by the PI control).
i = Tp × α is calculated, and a drive pulse signal having a pulse width corresponding to Ti is output to the fuel injection valve 15 at a predetermined timing synchronized with the engine rotation to perform fuel injection.

The control unit 11 for controlling HC adsorption / desorption and the control unit 16 for controlling the engine are connected by a communication line 18. FIG. 3 is a flowchart of the HC adsorption / desorption control executed by the control unit 11. In step 1 (indicated as S1 in the figure. The same applies hereinafter), the start switch is turned on.
If it is determined to be OFF and the start switch is turned ON, the process proceeds to step 2 and subsequent steps.

In step 2, the flow path switching valve 8 is connected to the main passage 5
Is closed and the sub passage 6 is opened. As a result, all the exhaust gas from the engine 1 is diverted to the sub-passage 6 and circulated to the adsorbent 7. Therefore, at the time of starting and immediately after starting, and while the main catalyst 4 is not activated, HC in the exhaust gas is adsorbed by the adsorbent 7 and is prevented from being released to the atmosphere.

In step 3, the adsorbent inlet exhaust temperature sensor 12
Adsorbent inlet exhaust temperature Ta is detected a predetermined value to determine whether it is above T ₁ (HC desorption temperature of the adsorbent), holds the switching state of the Step 2 until reaching Thus, reaches If so, go to step 4. In step 4, the flow passage switching valve 8 is switched to open the main passage 5 and close the sub passage 6.

That is, when the adsorbent inlet exhaust temperature Ta becomes equal to or higher than the predetermined value T ₁ after warming up to some extent, the adsorbent 7 loses its adsorbing ability and the main catalyst 4 is considerably activated. Therefore, in order to terminate the adsorption of HC and prevent desorption, the main passage 5 is opened and the sub passage 6 is closed. As a result, all the exhaust gas from the engine 1 is sent to the main catalyst 4 through the main passage 5 without being diverted to the sub passage 6.

In step 5, it is judged whether or not the main catalyst outlet exhaust temperature Te detected by the main catalyst outlet exhaust temperature sensor 13 has become a predetermined value (catalyst activation temperature) T ₂ or more,
Until this is reached, hold the switching state in step 4,
When reached, proceed to step 6. In step 6, the flow passage switching valve 8 is switched so that the main passage 5 is closed and the sub passage 6 is opened.

That is, when the warm-up is completed and the main catalyst outlet exhaust temperature Te exceeds the predetermined value T ₂ , the main passage 5 is closed and the sub-passage 6 is opened for the desorption process of HC. . As a result, the exhaust gas from the engine 1 is diverted to the sub-passage 6 and circulated through the adsorbent 7, and then discharged through the main catalyst 4. Therefore, the HC adsorbed on the adsorbent 7 is desorbed, and the desorbed HC is introduced into the main catalyst 4 and purified.

At the time of this desorption process, simultaneously with the execution of step 6, steps 7 and 8 are executed. In step 7, the air pump 9 is operated to introduce secondary air from the secondary air inlet 10 to the upstream side of the main catalyst 4.
This portion corresponds to the secondary air introduction means during desorption.

In step 8, a signal is sent to the control unit 16 for controlling the engine via the communication line 18 to change the PI constant, which is one of the fuel injection amount control constants. Increase the injection amount. This portion corresponds to the air-fuel ratio enrichment means during desorption. That is, during the desorption process, a sufficient amount of secondary air for obtaining active combustion in the main catalyst 4 is introduced from the upstream side of the main catalyst 4 to enhance the HC purification performance in the main catalyst 4, and A rich shift is applied by changing the PI constant, which is one of the fuel injection amount control constants. The PI constant is the O ₂ sensor.
According to the judgment of rich lean based on the signal from 17,
It is an increase / decrease value when the air-fuel ratio feedback correction coefficient α is increased / decreased, and a PI constant used when increasing the air-fuel ratio feedback correction coefficient α during lean determination is used as a PI constant used when decreasing the air-fuel ratio feedback correction coefficient α during rich determination. Rich shift is possible by making it larger than a constant.

Here, FIG. 5 (a) shows how the main catalyst inlet air-fuel ratio and the main catalyst outlet NOx change when secondary air is introduced (when the air-fuel ratio is not made rich) during the desorption process, FIG. 5B shows how the main catalyst inlet air-fuel ratio and the main catalyst outlet NOx change when the secondary air is introduced and the air-fuel ratio is made rich during the desorption process.

As described above, during the desorption process of the adsorbent and at the time of introducing the secondary air, the PI constant is changed and the rich shift is performed, so that the secondary air is introduced during the desorption process to create a lean atmosphere. As a result, the air-fuel ratio at the inlet of the main catalyst, which has reduced NOx purification performance, is brought close to the stoichiometric air-fuel ratio to maintain good purification performance for the three components (HC, CO, NOx) in the catalyst, and at the same time, the atmosphere in the combustion chamber is rich. As a result, the amount of NOx generated from the engine also decreases, and as a result of these, NOx
It is possible to perform the desorption process of the adsorbent without increasing the discharge amount of the adsorbent.

As a method of applying the rich shift during the desorption process, there are methods such as changing the base air-fuel ratio and changing the slice level of the O ₂ sensor, in addition to changing the PI constant. In step 9, it is determined whether or not the desorption process has been completed based on the elapse of time, the temperature of the adsorbent, and the like.

In step 10, the flow path switching valve 8 is connected to the main passage 5
Is opened and the sub passage 6 is closed, and
The secondary air introduction by the air pump 9 is stopped, and the communication line
The PI constant is returned to the original value via 18, and this routine ends. FIG. 4 shows another mode of the flowchart of the HC adsorption / desorption control. Here, the steps 6 ′ to 8 ′ executed during the desorption process are different from those in FIG. 3, and this part will be described.

When the activity of the main catalyst 4 is judged,
First, in step 6 ′, a signal is sent to the control unit 16 for controlling the engine via the communication line 18 to change the PI constant, which is one of the fuel injection amount control constants,
The fuel injection amount from the fuel injection valve 15 is increased to enrich the air-fuel ratio. Then wait for an appropriate time. After that, in step 7 ′, the flow path switching valve 8 is switched so as to close the main passage 5 and open the sub passage 6, so that the exhaust gas is adsorbed by the adsorbent 7
And at the same time, in step 8 ', the air pump 9
Is operated to introduce the secondary air from the secondary air inlet 10 to the upstream of the main catalyst 4.

That is, prior to the desorption process, the air-fuel ratio is made rich to minimize the NOx emission amount. That is, as shown in FIG. 5 (b), the effect of enrichment is delayed, and the NOx emission amount increases during that time, so that the air-fuel ratio is enriched prior to the desorption process.
As shown in (c), the amount of NOx emissions is minimized.

Next, another embodiment will be described. FIG. 6 shows a system configuration of another embodiment, and only parts different from those in FIG. 2 will be described. An EGR passage 21 that guides a part of the exhaust gas from the exhaust passage 2 (upstream of the pre-catalyst 3) of the engine and recirculates it to the intake passage 14 is provided.
An R control valve 22 is interposed. The EGR control valve 22 is controlled by a control unit 23 for controlling the engine.

The control unit 23 has a built-in microcomputer, into which various kinds of information are input, and the EGR control valve 22 is subjected to predetermined arithmetic processing.
To control the EGR amount and the EGR amount. The control unit 11 for controlling HC adsorption / desorption and the control unit 23 for controlling the engine are connected by a communication line 24.

FIG. 7 is a flow chart of the HC adsorption / desorption control executed by the control unit 11, and only parts different from FIG. 3 will be described. In step 8, instead of increasing the fuel injection amount, a signal is sent to the control unit 23 for engine control via the communication line 24, the opening degree of the EGR control valve 22 is increased, and the EGR amount is increased. This portion corresponds to the EGR amount increasing means during desorption.
In step 10, instead of stopping the increase of the fuel injection amount, the increase of the EGR amount is stopped.

That is, in this embodiment, the NOx discharged from the engine is reduced by increasing the EGR rate during the desorption process and during the introduction of the secondary air.
This can be explained as follows. Assuming that the NOx emission concentration from the engine 1 during normal operation is 100, x by the pre-catalyst 3
Assuming that 100% is purified, the NOx emission concentration at the outlet of the pre-catalyst 3 becomes the following (1).

100 × (1-x / 100) (1) Further, assuming that y% is purified by the main catalyst 4, the NOx emission concentration at the outlet of the main catalyst 4 is the following (2).
Becomes 100 × (1-x / 100) × (1-y / 100) (2) However, by introducing the secondary air upstream of the main catalyst 4 during the desorption process, the NOx purification rate of the main catalyst 4 is z. %, The NOx emission concentration at this time is (3) below.

100 × (1−x / 100) × (1−z / 100) (3) Here, since z <y, (3)> (2), and thus NO.
x emission concentration increases. Therefore, during the desorption process,
Increase the EGR rate to increase the NOx emission concentration from the engine.
By lowering the value from 100 to 100-A as shown in (4) below, the deterioration of the NOx purification rate of the main catalyst 4 is compensated for, and an increase in the NOx emission amount is prevented. (100 −A) × (1−x / 100) × (1−z / 100) (4) As shown in the flowchart of FIG. 8, when the activity of the main catalyst 4 is determined, first, In step 6 ',
The opening degree of the EGR control valve 22 is increased to increase the EGR amount, and after waiting an appropriate time, the flow passage switching valve 8 is closed in the main passage 5 and the sub passage 6 is opened in step 7 ′. The exhaust gas may be switched to guide the adsorbent 7, and at the same time, in step 8 ′, the air pump 9 may be operated to introduce the secondary air from the secondary air inlet 10 to the upstream of the main catalyst 4. .

[0035]

As described above, according to the present invention, N
The effect that it becomes possible to favorably carry out the desorption treatment of HC from the adsorbent without increasing the amount of Ox discharged is obtained.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention.

FIG. 2 is a system configuration diagram showing an embodiment of the present invention.

FIG. 3 Flow chart of HC adsorption / desorption control

FIG. 4 is a flowchart showing another aspect of HC adsorption / desorption control.

FIG. 5 is a diagram showing the effect of introducing secondary air and enriching the air-fuel ratio.

FIG. 6 is a system configuration diagram showing another embodiment.

FIG. 7 is a flow chart of HC adsorption / desorption control in another embodiment.

FIG. 8 is a flowchart showing another aspect of HC adsorption / desorption control in another embodiment.

[Explanation of symbols]

1 engine 2 exhaust passage 3 pre-catalyst 4 main catalyst 5 main passage 6 auxiliary passage 7 adsorbent 8 flow path switching valve 9 air pump 10 secondary air inlet 11 control unit 12 adsorbent inlet exhaust temperature sensor 13 main catalyst outlet exhaust temperature sensor 14 Intake passage 15 Fuel injection valve 16 Control unit for engine control 17 O ₂ sensor 18 Communication line 21 EGR passage 22 EGR control valve 23 Control unit for engine control 24 Communication line

Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location F01N 3/32 ZAB 301 C F02D 41/06 330 B 8011-3G 43/00 301 H 7536-3G N 7536-3G T 7536-3G F02M 25/07 550 R

Claims (2)

[Claims] 1. A sub-passage is provided in parallel with a main passage of an exhaust passage upstream of a catalyst for purifying exhaust gas, and a hydrocarbon adsorbent is interposed in the sub-passage, while the main passage and the sub-passage are provided. To control the flow of exhaust gas to the exhaust gas, and by controlling this valve device, all of the exhaust gas is circulated to the adsorbent to adsorb hydrocarbons in the exhaust gas when the engine is cold, and after warm-up is complete. In an exhaust gas purification apparatus for an internal combustion engine, comprising: a control device that causes at least a part of exhaust gas to flow through an adsorbent at one time to desorb hydrocarbons, when desorbing hydrocarbons from the adsorbent by the control device, The desorption secondary air introduction means for introducing the secondary air to the catalyst is provided, and the desorption air-fuel ratio enrichment means for controlling the air-fuel ratio of the engine intake air-fuel mixture to the rich side at the desorption is provided. An exhaust purification device for an internal combustion engine. 2. A sub-passage is provided in parallel with the main passage of the exhaust passage upstream of the exhaust purification catalyst, and a hydrocarbon adsorbent is interposed in the sub-passage, while the main passage and the sub-passage are provided. To control the flow of exhaust gas to the exhaust gas, and by controlling this valve device, all of the exhaust gas is circulated to the adsorbent to adsorb hydrocarbons in the exhaust gas when the engine is cold, and after warm-up is complete. In an exhaust gas purification apparatus for an internal combustion engine, comprising: a control device that causes at least a part of exhaust gas to flow through an adsorbent at one time to desorb hydrocarbons, when desorbing hydrocarbons from the adsorbent by the control device, A secondary air introduction means for desorption for introducing secondary air into the catalyst is provided, and an exhaust recirculation quantity increasing means for desorption at the time of desorption for controlling the exhaust gas recirculation quantity to be recirculated from the exhaust passage to the intake passage at the time of desorption. Of internal combustion engine characterized by the provision of Qi purification device.